The invention relates to a bushing for a drive unit, in particular an eccentric bushing for a wiper drive of a windshield wiper. The invention furthermore relates to a drive unit, in particular a wiper drive for a windshield wiper of a motor vehicle.
The German patent publication DE 103 13 734 A1 discloses an electric drive unit for windshield wipers of a motor vehicle, said drive unit comprising an electric motor, which drives a worm wheel of a gear assembly via a drive shaft with a worm. The worm wheel is mounted in an eccentric bushing, which in turn is seated in a stepped mounting hole of a gear assembly housing. Corresponding to the stepped mounting hole in the housing, the eccentric bushing comprises in addition to a flange section a correspondingly stepped mounting section, which has a first press region adjacent to the flange section, an intermediate region and a second press region at the free longitudinal end section. In order to mount the eccentric bushing, the two press regions are press fitted into corresponding press regions of the stepped mounting hole, wherein a collar of the flange section of the eccentric bushing comes flatly to rest at an edge of the mounting hole.
The use of an eccentric bushing is therefore necessary because a distance between the drive shaft and the worm wheel must be precisely set in order on the one hand to be able to reliably and permanently transmit high torques and on the other hand to be able to fulfill the requirements with regard to noise emissions. A problem with the mounting of the eccentric bushing is that the intermediate region is designed in such a way that in the mounted state, the same is disposed without contact to the mounting hole and therefore an air volume is enclosed in said mounting hole between the two press regions. During the mounting process a rapid compressing action of this air volume can occur, which produces a force opposite to the mounting direction of the eccentric bushing. This opposing force can be so great that the eccentric bushing can no longer be correctly mounted. In the case of a mounted eccentric bushing, a further problem is that water can seep inwardly into the housing through capillaries formed between the collar of the flange section and the flat contact surface on the gear assembly housing.